Must-See: President Obama Delivers Second Inaugural Address

Today, President Barack Obama was sworn in to serve his second term as 44th president of the United States. He accepted the oath of office and delivered his inaugural address as 800,000 people watched from the National Mall in Washington, D.C.

During the Constitutionally-required oath, administered by Chief Justice John Roberts, President Obama placed his hand on two Bibles — one which was formerly owned by Abraham Lincoln and another by Rev. Martin Luther King Jr.

"Each time we gather to inaugurate a president, we bear witness to the enduring strength of our Constitution," President Obama said at the beginning of his speech. "We affirm the promise of our democracy. We recall that what binds this nation together is not the colors of our skin or the tenets of our faith or the origins of our names."

During his inaugural address, Obama urged Americans to confront the country's current economic and social challenges. He also made references to the recent shooting at Sandy Hook Elementary and the Stonewall gay-rights riots of 1969.

His address was followed by the singing of “My Country ‘Tis of Thee" by Kelly Clarkson and "The Star Spangled Banner" by Beyonce Knowles-Carter.

President Obama and Vice President Joe Biden were both officially sworn in during private ceremonies on Sunday. The president took his oath alongside First Lady Michelle Obama and daughters Sasha and Malia in the Blue Room of the White House. The vice president was sworn in at his residence on the grounds of the Naval Observatory.

Before the public inauguration ceremony began today, President Obama took to Twitter to express his gratitude. “I’m honored and grateful that we have a chance to finish what we started,” he wrote. “Our work begins today. Let’s go. —bo.”